Most owners who have had difficulties with AM audio quality have
reported that the 6 kHz option AM filter (p/n XF112A) is an absolute necessity
for both transmitting in AM. It also makes the FT840 an excellent SWL receiver. Use of a AM modulation meter can tell you the percent of modulation your AM signal is peaking at. Ideally, you're looking for 100% modulation; over 100% the signal get distorted, under 100%, the signal sounds weak. For more information on running AM in the ham bands, go to The AM Window, where there's info on frequencies, audio tips, and running modern solid-state rigs on AM.

Want to make your radio do more than what it came with out of the box? Or are you running a transverter and want to get complete band coverage?
This mod will reprogram the Yaesu FT840 ham rig to transmit from 1.8-30 mHz
with NO GAPS. It doesn't require any desoldering, diode snipping or clipping,
or even any rewiring (other than a temporary ground jump), and can be done by
anyone with a basic knowledge of electronics.

Tools Required:

1 Set of small alligator-clip jumper leads (Radio Shack, RS# 278-1157)
1 Small Phillips head screwdriver

Time: 15 minutesDifficulty: Easy

1. Remove antenna from radio and disconnect power supply.
2. Remove top and bottom covers.
3. Jump test point TP-2003 to ground.
(Take a wire lead + attach to the metal case)
4. Press & Hold (SSB) + (AM) and turn power on. (Display will show 02-OFF)
5. Rotate main control to show 02-ON
6. Press AM. The display should read (7.000.00 LSB)
7. Turn radio OFF.
8. Press and hold the memory (DOWN) + (UP) buttons and turn radio ON.
9. Turn the radio OFF.
10. Remove the jumper to ground on TP-2003.
11. Reassemble radio.
12. Reconnect antenna and power supply.

TP-2003 is a small pin next to the round backup battery. You have to remove both the top and bottom covers, even though the pin itself is on the bottom side of the chassis. Remove the top cover first; it locks itself into the bottom cover. You don't need to disconnect the speaker leads going into the top-mounted speaker.

Remember to use large diameter zip cord when using the FT840; total
current draw at 100 watts SSB can exceed 20 amps. Use of a ferrite RF line
choke (Radio Shack, RS 900-7042) will reduce power hum from a dirty power
supply.

Although it wasn't designed as a ground station rig for satellite operations, the FT840 can operate
as an IF receiver for a VHF/UHF transverter, or a seperate receiver for Mode A
(2 meters for the uplink, 10 meters for the downlink) if you already have a 2 meter rig for the
uplink frequency. A 10 meter dipole will receive the downlink signals from LEO satellites
such as the Russian Radio Sputnik series very well. Go to AMSAT's web
site for more information about satellites, frequencies, times, modes, etc.